Why not just stick with thicker ropes and familiar belay devices?
It's an option. The thinner ropes weigh less. If you do a long pitch and have two 50m lengths of rope hanging off you, you might notice it. For example, two 50m lengths of Beal Ice line (8.1mm) is 2.5 lbs lighter than the same lengths of Beal Joker (9.1mm). 50m of the Ice lines are going to weigh you down to the tune of about 9.25 lbs, the same length Jokers about 11.7 lbs.